This invention relates to a device for the centered clamping, in a lathe, of annular workpieces, particularly split, radially resilient piston rings. The device is of the type that has an axially displaceable centering cylinder as well as two clamping discs which are adapted to engage the workpiece or the workpiece stack at opposite end faces and axially clamp the same by means of a tensioning anchor extending within the hollow work spindle of the machine tool.
German Pat. No. 1,014,410 discloses a device for the centered clamping of resilient rings, particularly piston rings, on a tensioning mandrel. The device is formed of a mandrel sleeve, an internal pull rod as well as a first clamping disc insertable on the mandrel sleeve and a second clamping disc which may be connected with the pull rod for axially clamping a piston ring stack between the clamping discs. For the centering of the radially resilient piston rings there is provided a centering sleeve which may be inserted over the clamping mandrel and the piston ring stack and which, subsequent to the axial clamping of the piston ring stack, may be removed therefrom.
In practice, the clamping mandrel of the above-outlined known device is connected with the rotary work spindle of a turning machine, such as a lathe. In this arrangement the pull rod extends axially through the conventionally hollow work spindle and is actuated by means of a clamping cylinder disposed at the opposite end of the machine. The centering sleeve is connected indirectly with the machine bed by means of the headstock and is, together with the latter, axially displaceable relative to the machine bed.
The above-outlined device has the disadvantage that for replacing the piston ring stack, not only has one clamping disc to be manually removed from the pull rod terminus, but the piston ring stack first has to be stripped from the mandrel sleeve prior to its removal in the radial direction. The new piston ring stack to be machined has to then be mounted on the clamping mandrel in a reverse order.
There are, to be sure, known machines of a different type in which the piston rings, individually or in a stack, may be radially introduced between two clamping discs and then axially clamped thereby. Such special machines, however, need a bilateral support and guidance of the tensioning (clamping) means which not only is very expensive, but is liable to possible additional malfunctioning, particularly in view of the large axial tensioning force having its path externally and eccentrically of the piston ring stack.